Camshaft sensor - inductive

The purpose of this test is to evaluate the operation of an inductive Camshaft Position (CMP) sensor from its output voltage.

How to perform the test

View connection guidance notes.

1. Use manufacturer’s data to identify the CMP sensor signal circuit.
2. Connect PicoScope Channel A to the sensor signal circuit.
3. Start the engine and run at idle.
4. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
5. Start the scope to see live data.
6. With your waveform on screen stop the scope.
7. Stop the engine.
8. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Waveform notes

This known good waveform has the following characteristics:

• A periodic event, similar to a single sine wave cycle, occurring once every 720 degrees of crankshaft rotation (i.e. once per 360 degrees of camshaft rotation).
• As engine speed increases, amplitude and frequency increase.
• There is no excessive noise or inconsistent breaks in the waveform.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select Camshaft sensor (Inductive).

Further guidance

A CMP sensor signals one or more fixed camshaft reference positions to the Engine Control Module (ECM), for example, the arrival of cylinder one intake stroke.

A CMP sensor is sometimes referred to as a Cylinder Identification (CID) sensor or phase sensor.

The ECM uses the camshaft sensor signal for accurate timing control of ignition, injection, and variable valve phasing, etc.

An inductive CMP sensor consists of a circuit with a wire coil around a magnet. The sensor is accompanied by a reluctor ring, or trigger wheel, attached to the camshaft. The reluctor ring or trigger wheel, which may be configured with one or more teeth, holes or slots, periodically disturb the sensor’s magnetic field to induce a circuit voltage. The induced voltage depends on engine speed: the faster the camshaft rotates, the greater the magnetic field disturbance.

If a unique reference mark exists for each cylinder, the camshaft position sensor signal can be used as a rapid start phase sensor: with this configuration, a 4-cylinder engine can start within 180 degrees of crankshaft rotation (90 degrees of camshaft rotation).

A faulty camshaft sensor can cause multiple misfires, loss of engine performance, engine cutting out, limp-home mode operation, or engine cranking but not starting symptoms.

Possible faults are:

• Short or open circuits and high resistance in the sensor coil or circuit.
• Reduced sensor output due to excessive dirt and detritus on the sensor housing or reluctor.
• Incorrect fitment or operation of the sensor or camshaft components, causing:
  • excessive gaps between the sensor and reluctor
  • damage to the sensor housing or reluctor
  • excessive camshaft movement or vibration

GT011